In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occured in the rodent populations following the accident?

a.) Mutations caused major changes in rodent physiology over time.

b.) Mutation caused genetic drift and decreased fitness.

c.) Mutation caused the fixation of new alleles.